1. Field of the Invention
The present invention relates to a writing implement provided with a shaft tube formed in a cylindrical shape, in which a part at an end of the shaft tube that most of the users grip is formed as a reduced-diameter portion with a diameter smaller than an outside diameter of the remaining part, and in which a cylindrical grip member made flexible elastic material is fitted to the reduced-diameter portion.
2. Description of the Related Art
There has been conventionally used a writing implement fitted with a flexible grip member in the vicinity of a tip end of its shaft tube where a user is likely to hold lest a grip should slip or hurt the user's fingers when being used to write for a long time,
More specifically, a tip-end part of a shaft tube of a writing implement formed in a cylindrical shape has a reduced diameter, which is referred to as a reduced-diameter portion. The reduced-diameter portion of the shaft tube is covered with a grip member which is formed in a cylindrical shape having an inside diameter corresponding to the reduced-diameter portion.
As materials for the grip member, in general, flexible materials such as rubbers, e.g., silicone rubber, EPDM (ethylene-proplylene-diene rubber) and NBR (acrylonitrile-butadiene rubber), thermoplastic elastomers, etc. are used.
As the grip member, there are known those in which an end surface located in the middle-part side of the shaft tube is so formed as to be inclined with respect to a central axis of the shaft tube, that is, so as to be inclined from a vertical surface perpendicular to the central axis. If such a grip member is provided in the writing implement, it is possible to mitigate the pain in the fingers caused by writing for a long time due to the flexibility of the grip member and, in addition, it is possible to impart excellent design to the writing implement due to the inclined end surface.
In a writing implement provided with a grip member as described above, a tip member formed in a substantially conical shape is usually screwed to a tip-end portion of its shaft tube. In such a shaft tube, a step is formed at the boundary between a portion having a larger diameter than the reduced-diameter portion and the reduced-diameter portion. As a result, it is ensured that the grip member fitted to the reduced-diameter portion is supported by being interposed between the step of the shaft tube and the tip member.
If the whole length of the grip member is larger than the whole length of the reduced-diameter portion, then the grip member supported by being interposed between the step and the tip member is compressed by strongly fastening the tip member screwed to the shaft tube. Then, the grip member and the tip member engage frictionally with each other, and, as a result, the grip member prevents the tip member screwed to the shaft tube from rotating. Therefore, the screwed tip member does not become loose due to vibrations or the like, and it is possible to prevent troubles, such as unexpected disengagement of the tip member from the shaft tube during transfer (cf. JP 2007-253548 A).
In a writing implement as described above, in order to improve the appearance in terms of designing, a grip member whose end surface is inclined with respect to the central axis of the shaft tube (i.e., a grip member having an end surface inclined from a vertical surface perpendicular to the central axis) is adopted, then also a step surface formed at the boundary of the reduced-diameter portion provided in the shaft tube is so inclined as to correspond to the inclined end surface of the grip member.
The grip member, while disposed between the step surface of the shaft tube and the tip member, is supported by being interposed between the step surface of the shaft tube and the tip member by fastening the tip member screwed to the tip end of the shaft tube. As a result, the grip member is fixed in a compressed condition.
In a case where the step surface is inclined as described above, while fastening the tip member screwed to the tip end of the shaft tube, the inclined grip member cannot engage the tip end of the acute-angled end surface of the grip member and therefore, due to the fastening of the tip member, the tip end of the acute-angled end surface of the grip member moves along the inclined step surface and rises from the surface of the shaft tube. Due to the mounting of the grip member, therefore, contrarily troubles as described below occur. That is, the appearance of the writing implement is impaired and, besides, the end portion of the grip member becomes turned up and hence becomes apt to be damaged.
Thus, each aspect of the present invention was incorporated in the invention in view of the problems with the related art, and the object of the invention is to provide a writing implement capable of eliminating troubles caused by the adoption of a grip member having an end surface inclined from a vertical surface perpendicular to a central axis of a shaft tube.